There are numerous proposed schemes by which various natural ores, concentrates and slags may be processed for the recovery of metal values. Commercial schemes for the extraction and separation of tantalum and niobium values from beneficiated ores or from tin slags, are described in detail in U.S. Pat. Nos. 2,767,047; 2,953,453; 2,962,372; 3,117,833; 3,300,297; 3,658,511; 3,712,939 and 4,164,417. In these prior processes, feed solids were generally digested with hot, concentrated hydrofluoric acid to solubilize most of the tantalum and niobium values as fluorides. A liquor containing the dissolved metal values is separated from the undissolved solids and is treated in a multistage liquid-liquid extraction cascade wherein the metal values are extracted with methylisobutyl ketone (MIBK). The residue from the acid digestion process contains insoluble metals such as uranium and thorium, and also contains within the entrained insoluble matter quantities of dissolved tantalum and niobium. Stockpiling of these source materials results in the loss of revenues from the unrecovered metal values.
A general discussion of other ore process schemes is found in Extractive Metallurgy of Niobium, Tantalum and Vanadium, INTERNATIONAL METALS REVIEW, 1984, vol. 29, No. 26, BB 405-444, published by The Metals Society (London) and in The Encyclopedia Of Chemical Technology, 3rd ed., Vol. 22 pp 547-550.
Commonly assigned U.S. Pat. No. 5,023,059, entitled, "Recovery of Metal Values and Hydrothoric Acid from Tantalum and Columbian Waste Sludge" also discloses a method for the recovery of tantalum.
It is believed, therefore, that a process that would recover metal values from source materials that contain such metal values as complexed fluorides, that would provide for the recovery of acids from the source materials that would produce a solid waste residual which is non-hazardous under all EPA listings and characteristic tests, and low enough in uranium and thorium content to be suitable for disposal as low-level radioactive waste, would constitute a desirable advancement in the art.
It is an object of this invention to provide an efficient process for the recovery of metal values from source materials of the dissolution of ores and concentrates.
It is another object of this invention to provide an improved process for the recovery of metal values from dilute aqueous process streams.
It is a further object of this invention to recover portions of the sulfuric acid and hydrofluoric acid streams.
It is still another object of the present invention to provide a metal values recovery process, suitable for handling dilute source solids, that will generate solid and liquid waste products that are non-hazardous under EPA's toxic characteristic leaching procedure and all other EPA hazardous characteristics and listing, and that can therefore be disposed of legally either as low-level radioactive waste or as non-hazardous, non-radioactive waste.
It is yet a further object of the present invention to provide an efficient process for the recovery of metal values from source material of the dissolution and concentrates which results in reduced quantities of solid and liquid waste products.
Accordingly, the present invention comprises a process for recovering metal values from a source material containing at least tantalum or niobium and metallic fluorides where the source material is digested with sulfuric acid to form a slurry. The slurry, upon separation, has both a solid and a first liquid aqueous phase. The liquid phase is contacted with a water immiscible organic liquid suitable for extracting tantalum values. A first organic phase beating tantalum values and a second aqueous phase bearing uranium values is formed. The first organic phase is contacted with an aqueous liquid such as water to form a third aqueous phase containing the tantalum values. Tantalum values are then recovered from the third aqueous phase.
In an alternative embodiment, the separated solids from the digested source material are subjected to pyrohydrolysis. This process provides for the recovery of sulfuric and hydrofluoric acids from the solids and renders the leftover solid residuals non-hazardous under EPA listings and characteristic test, and therefore permissible for disposal as low level radioactive waste.
In another embodiment, the uranium bearing second liquid aqueous phase is brought into contact with an ion exchange resin to form a uranium depleted phase.